What defines the level of difficulty of a subject is entirely in the eyes of the beholder. To be a bit trite, maths/science-orientated individual may consider Methods, Specialist, Chem, Physics and Biology particularly easy for them, while one who enjoys humanities may consider English, Classics, etc. easy. Your proposition in a) is correct, but when measuring up the perceived level of difficulty in each unique case, the term 'simpler' becomes subjective as everyone would have different views on different subjects according to what their interests/strengths are. But I agree with b). I think you should alter your theory to say there's no such thing as a subject that has an unfair advantage in terms of scaling, but that is a bit controversial too considering all the qualms about scaling over 50.